1. Field of the invention
The invention relates to a turboshaft engine having a stator equipped with means for preventing the longitudinal or axial flow of gas around the guide vane stages of the stator.
2. Summary of the prior art
The stator of many turboshaft engines comprises a double envelope formed by an outer casing and a ring which is surrounded by the casing and which is constituted by a plurality of interconnected elements to which the vanes of the guide stages are secured. The ring elements are screwed to the casing and are provided with radially-extending circumferential ribs which engage the casing to maintain the spacing between the ring and the casing. However, as these ribs are the cause of a substantial outward heat loss by virtue of their good thermal conductivity, they are provided with apertures so that they only touch the casing at circumferentially spaced positions. The drawback with this arrangement is that the volume between the ring and the outer casing becomes continuous, with the result that it becomes impossible to achieve fine adjustment of the clearance between the rotor blades and each ring element by blowing heating or cooling gas at different temperatures or rates into different sections of the volume between the casing and the ring in order to vary the thermal expansion of each ring element independently. Only an overall setting is possible, and this fails by far to provide the same degree of precision in reducing clearances to a minimum, so that the output of the engine is affected. Re-establishment of a seal at each rib is therefore desirable in order to prevent the axial flow of gas between the casing and the ring elements through the apertures of the ribs. Several solutions have been proposed in French Patents Nos. 2468738, 2482661 and 2575221, and in U.S. Pat. No. 4,314,793, but are generally fairly complicated. The aim of the invention is to provide a particularly simple solution to this problem.